Polyamidoimide resins exhibit excellent heat stability, since they contain a combination of an aromatic nucleus and an imido bond. Furthermore, they exhibit excellent toughness because of the high flexibility thereof, which is believed to be attributable to the amido bond. In addition, they have excellent chemical resistance, abrasion resistance, and so forth. Thus, they are very useful engineering plastics.
These polyamidoimide resins are usually molded into various molds or articles by injection molding. However, extruded articles such as continuous bars and pipes, and articles having variable cross sections have not yet been produced from the polyamidoimide resins. This is due to the fact that the polyamidoimide resins cannot be satisfactorily extruded by conventional extrusion molding processes, and even if they could be molded, the molded articles obtained would have only a relatively low density and poor surface characteristics, e.g., appearance.